1. Field of the Invention
The present invention relates to a thermal transfer type printing device, in particular, a character printer comprising a thermal head for use in printer, copier, facsimile device, etc. and ink medium such as ink ribbon, ink sheet or the like.
2. Description of the Prior Art
Various types of character printing devices comprising a thermal head have been used heretofore in the field of printer, copier, facsimile device, etc. In the case of printing characters by use of thermal head, an ink sheet is heated by the thermal head and the heated sheet makes a pressed contact with recording paper. Printing of characters is performed in such a way.
Various different printing processes are well known in the past. Namely, those are the processes of printing characters by use of an ink sheet containing therein various species of ink: thermofusible ink, sponge ink and sublimation ink, etc.
Those species of ink have their own inherent characteristics in accordance with the respective ink processes. For instance, although the thermofusible ink is suitable for printing characters, it isn't suitable for printing full-color picture image because of its incapability of expressing halftone in the case of printing picture images. On the contrary, the sublimation ink can easily express halftone. In consequence, the same is suitable for printing full-color picture image. However, it takes a lot of time to develop color on the recording sheet owing to its characteristic of image processing compared with the case of using the thermofusible ink, so that the sublimation ink isn't suitable for printing characters. The sponge ink has characteristic intermediate between that of the thermofusible ink and that of the sublimation ink. Since the conventional (prior art) printing device is so constructed as to fit to either one sort of ink processes, it follows that the printing device is properly used in accordance with its use. As a result, interface of respective printing devices has to be changed, and further the size of paper has to be also changed. In such a way, it is very inconvenient to use the conventional printing device.
In addition to the above-mentioned, generally, a printing device in which a printing head constructed with, for instance, a thermal head is pressedly brought into contact with a platen through an ink sheet and a recording paper is well known heretofore. Such kind of printing device is constructed, for instance, for use in facsimile, printer, copier and so on. Generally, in such printing device, the ink sheet is assembled in a state of being accommodated in a cassette. In such printing device, a print control is performed in accordance with the sort of ink sheet by use of a cassette accommodating various different kinds of ink sheet. For instance, the Japanese laid-open patent specification; Showa 60-230765/1985 discloses that, in the ordinary thermal transfer type printer, the pulse width of the applied voltage is changed in accordance with the sort of paper such as ordinary paper employed for printing or transfer paper especially employed for making OHP film, and thereby the optical density corresponding to its purpose can be obtained.
In the case of employing the cassette accommodating such ink sheet, since the cost of the cassette case itself is relatively high compared with the cost of ink sheet, the above-mentioned matter results in the increase of print cost. It is considered to be a demerit of such the printing device. In consideration of such actual situation as mentioned above, it may be profitable from the viewpoint of its cost to install the ink sheet itself, for instance, as an ink sheet roll in the printing device's main body. However, there is no printing device provided with means capable of automatically judging the sort of ink in the past. Although the construction in which the selection switch mounted on the operational panel designates manually the print mode of several sorts of ink sheet has been adopted heretofore to take an illustration, there was a fear of performing other different print control in such the adopted construction of process (mode) was done in a wrong way.